This invention relates to manufacture of power transmission belting, such as the side drive type or positive drive type, having stable length tensile members disposed within an elastomeric belt body.
Power transmission belting is normally produced by superimposing alternate layers of rubber or rubber-like material and/or fabric on a bulding drum, with an interposed embedded tensile reinforcement, which may be applied during the building process as spirally wound cord. The resultant sleeve of uncured belting is removed from the building drum and either (1) directly cured as a sleeve within a suitable mold, from which one or more raw edge or bandless type belts may be formed, or (2) cut into individual belt segments and cured in a segmented or ring type mold, particularly (though not necessarily) for the production of belting having an outer wrap fabric cover.
With either of the mentioned manufacturing techniques, attention must be focused on any shrinkage or expansion properties of the tensile reinforcements. The thermal shrinkage or expansion properties of such tensile cord materials as nylon, cotton and polyester are generally used to advantage to mold the product and place both the overcord and undercord in a state of compression during curing. However, with stable length reinforcements, the tensile member does not extend or contract appreciably during the curing regime, whereby oftentimes either the undercord or overcord is not sufficiently compressed during molding. Such stable length tensile members also have the undesirable tendency to buckle when employing a mandrel type cure with an elastomeric air bag or bladder disposed outwardly of the sleeve (and mandrel).
Furthermore, prior art techniques for molding belt bodies having expansible or shrinkable tensile members do not satisfactorily place the tensile members in tension during curing, or do not produce a finished belt having an outside circumference within desired tolerances.
The present invention primarily overcomes these problems by applying both inwardly and outwardly directed pressures against the belt body simultaneously during curing, and applying a differential pressure outwardly against the body so as to tension the tensile members throughout the curing period in which the elastomeric rubber material is in its fluid or plastic state. Examples of the prior art include U.S. Pat. Nos. 2,573,642 to Hurry, 2,883,701 to Sauer, 3,078,205 to Sauer et al, and 3,398,218 to Richmond.